In this application we will examine the interaction between chronic stress and nicotine by studying behavior, autonomic responses, and hormone and neurotransmitter levels in several mouse models. This proposal arises from the finding that smokers often report an anxiolytic effect of cigarettes, and stress-related disorders such as depression, posttraumatic stress syndrome, and anxiety are often associated with chronic nicotine use. The influence of nicotine might depend on its ability to both activate and desensitize nicotinic acetylcholine receptors (nAChRs) in stress-related neural circuits. That basic action of nicotine, in turn, depends on the subunit composition of nAChRs that modulate those neural circuits. A related phenomenon is that chronic exposure to stress produces neural adaptations in brain regions that are associated with the rewarding effects of nicotine. To determine which nAChR subtypes are important for the interaction between stress and nicotine's actions, we will expose nAChR mutant mice lacking one or combinations of nAChR subunits to chronic stress. Our experiments will capitalize on the anxiety-related phenotypes that we and others have reported in nAChR mutant mice. The application also will address gender differences in the stress/nicotine interaction. Gender plays a major role in stress integration and stress-related affective disease states. We will investigate gender-related mechanisms by performing our experiments in ovariectomized and orchiectomized animals. Particular attention will be paid to the role of progesterone in the physiological mechanisms underlying stress by analyzing mice lacking the progesterone receptors A and B alone or in combination. The proposal will begin by examining the effects of chronic stress on nAChR mutant mice and their wild-type littermates. The other two main aims will examine the interaction between stress and nicotine. The second aim will examine how chronic stress affects the response to acute doses of nicotine. The third aim will examine the behavioral and physiological manifestations produced by chronic nicotine with and without concomitant exposure to stress. Our in vivo studies will combine behavioral testing with telemetry and the measurement of plasma levels of stress hormones. The in vitro studies will use in situ hybridization, autoradiography, and immunohistochemistry techniques.